MAINTENANCE OF THE M2 MACHINEGUN - Modern Prepper

SUBCOURSE 

OD1503 

EDITION 

A 

MAINTENANCE OF THE M2 MACHINEGUN

US ARMY TANK TURRET REPAIRER 

MOS/SKILL LEVEL: 45K30 

MAINTENANCE OF THE M2 MACHINEGUN 

SUBCOURSE NO. OD1503 

US Army Correspondence 

Course Program 

7 Credit Hours 

GENERAL 

The purpose of this subcourse is to provide knowledge of the 

components, operation, inspection and maintenance procedures for the 

M2 machinegun. 

The scope of this subcourse broadly covers the components, operation, 

inspection and maintenance procedures for the M2 machinegun. 

Seven credit hours are awarded for successful completion of this 

subcourse. It consists of one lesson with two tasks. 

Lesson 1: THE COMPONENTS, OPERATION, INSPECTION, AND MAINTENANCE 

PROCEDURES FOR THE M2 MACHINEGUN 

TASK 1: 

machinegun. 

Describe the components and operation of the M2 

TASK 2: Describe the inspection and maintenance procedures for the 


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M2 MACHINEGUN MAINTENANCE 

TABLE OF CONTENTS 

Section 

Page 

TITLE......................................................... 

TABLE OF CONTENTS ............................................ 

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Lesson 1: THE COMPONENTS, OPERATION, 

INSPECTION, AND MAINTENANCE 

PROCEDURES FOR THE M2 

MACHINEGUN ......................................... 1 

Task 1: Describe the components and 

operation of the M2 machinegun........................... 1 

Task 2: Describe the inspection and 

maintenance procedures of the M2 

machinegun............................................... 42 

Practical Exercise 1 .................................... 69 

Answers to Practical Exercise 1 ......................... 71 

REFERENCES ................................................... 73 

* * * IMPORTANT NOTICE * * * 

THE PASSING SCORE FOR ALL ACCP MATERIAL IS NOW 70%. 

PLEASE DISREGARD ALL REFERENCES TO THE 75% REQUIREMENT. 

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When used in this publication “he,” “him,” “his,” and “men” represent 

both the masculine and feminine genders, unless otherwise stated. 

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STUDENT NOTES 

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M2 MACHINEGUN MAINTENANCE - OD1503 - LESSON 1/TASK 1 

LESSON 1 

THE COMPONENTS, OPERATION, INSPECTION, AND 

MAINTENANCE PROCEDURES FOR THE M2 MACHINEGUN 

TASK 1. 

Describe the components and operation of the M2 machinegun. 

CONDITIONS 

Within a self-study environment and given the subcourse text, without 

assistance. 

STANDARDS 

Within three hours 

REFERENCES 

No supplementary references are needed for this task. 

1. Introduction 

The M2 caliber .50 machinegun supports the infantryman in both the 

attack and defense. It provides the rifleman with the heavy volume 

of close, accurate, and continuous fire necessary to accomplish his 

mission in the attack. The long range, close defensive, and final 

protective fires delivered by this weapon form an integral part of 

the unit's defensive fires. 

The M2 caliber .50 machinegun is also used to provide protection for 

motor movements, vehicle parks, and train bivouacs. It is also used 

to defend against low-flying hostile aircraft and to destroy lightly 

armored vehicles. In addition, it is used for reconnaissance by fire 

on suspected enemy positions. 

From these brief statements it is easy to see that the M2 is a 

vital and valuable piece of equipment, not only to the 

infantryman, but also to almost everyone in the Army who may find 

themselves in a combat situation. For this weapon to accomplish 

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its mission, it needs first rate care. That is the purpose of this 

subcourse, to describe the procedures used to inspect and maintain 

the M2 machinegun. However, before the weapon can be inspected and 

maintained, repair personnel must be familiar with the components and 

operation of the weapon. This task will introduce the student to the 

components and operation of the M2. 

2. Description 

a. Principles of Operation. The Browning machinegun, caliber .50 

heavy barrel (HB), M2, is a belt-fed, recoil-operated, air-cooled, 

crew-operated machinegun. The gun is capable of single shot, as well 

as automatic fire. 

(1) Belt Feed. By repositioning some of the component parts, the 

gun is capable of alternate feed (ammunition can be fed into the 

weapon from the left side or the right side of the receiver); 

however, the infantry uses only left side feed. A disintegrating 

metal link belt is used for feeding. 

(2) Recoil Operation. The force for recoil operation is furnished 

by expanding powder gases which are controlled by various springs, 

cams, and levers. 

(3) Air Cooling. Maximum surface of the barrel and receiver are 

exposed to permit air cooling. Perforations in the barrel support 

allow air to circulate around the breech end of the barrel and help 

in cooling the parts. The heavy barrel is used to retard early 

overheating. 

(4) General Data. The receiver alone weighs 60 pounds, while the 

barrel weighs 24 pounds. The weapon can be mounted on the M3 tripod 

with traversing and elevating mechanism. The tripod weighs 44 

pounds. When the machinegun is assembled and placed on the M3 

tripod, the total weight of the weapon is approximately 128 pounds. 

When firing M2 ball ammunition, the weapon has an approximate maximum 

range of 6,800 meters, while the maximum effective range of the 

weapon is 1,830 meters. The weapon can maintain a sustained rate of 

fire of 40 rounds or less per minute and a rapid rate of fire of 40 

rounds or more per minute. The cyclic rate of fire for the weapon is 

between 450 and 550 rounds per minute. The velocity of M2 ball 

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ammunition as it leaves the muzzle is 3,050 feet per second or 2,080 

mph. The overall length of the gun is approximately 65 inches with 

the length of the barrel being 45 inches. 

3. Function and Operation 

a. Functioning. The cycle of operation is broken down into eight 

basic steps. More than one step may occur at the same time. The 

steps are listed below and each step is explained before moving on to 

the next step. 

(1) Feeding. Feeding is the action of placing a cartridge in the 

receiver, approximately in back of the barrel, ready for chambering. 

When the bolt is fully forward, the belt feed slide is in the cover; 

the ammunition belt is held in the feedway by the belt holding pawl. 

As the bolt moves to the rear, the cam grooves guide the belt feed 

lever, pivoting the lever and moving the slide out of the side of the 

cover. The belt is held stationary by the belt holding pawl, while 

the belt feed pawl pivots, compressing its spring, and rides up over 

the link holding the first round. 

When the bolt is all the way to the rear, the belt feed slide moves 

out far enough to allow the belt feed pawl spring to force the pawl 

down behind the first round. As the bolt moves forward, the belt 

feed lever moves the slide back into the receiver. The belt is 

pulled in by the belt feed pawl. The next round rides over the belt 

holding pawl compressing its spring and forcing the pawl down until 

the round has passed over the pawl. 

When the bolt is fully forward, the slide is back in the cover; the 

first round is engaged by the extractor. If for any reason a round 

is not extracted from the belt, the belt feed pawl arm will ride up 

over the round, holding up the belt feed pawl to prevent double 

feeding. 

When withdrawing a round from the belt, the extractor grips the 

first round in the feedway and, as the recoiling parts move to the 

rear, withdraws it from the ammunition belt. Initially, the grip 

of the extractor is held secure by the downward pressure of the 

cover extractor spring. As the bolt continues its movement to the 

rear, the cover extractor cam forces the extractor down, causing 

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the cartridge to enter the T-slot in the bolt. As the bolt moves to 

the rear and the extractor is forced down, the extractor lug, riding 

along the top of the extractor switch, forces the rear end of the 

extractor switch downward. Near the end of the rearward movement, 

the extractor lug overrides the end of the switch and the switch 

snaps back up into position. 

(2) Chambering. As the bolt moves forward, the round is held by 

the T-slot and the extractor assembly. The extractor stop pin (on 

the left side of the bolt) permits the extractor assembly to go down 

only far enough to align the round with the chamber. As the bolt 

continues forward, the round is chambered. As this action takes 

place, the extractor lug rides up over the extractor cam, compressing 

the cover extractor spring, and through the pressure of the spring, 

snaps into the groove in the next cartridge base. 

(3) Locking. Initially, the bolt is forced forward in 

counterrecoil by the energy stored in the driving spring assembly and 

the compressed buffer disks. At the start of counterrecoil, the 

barrel buffer body tube keeps the accelerator tips from bouncing up 

too soon and catching in the breech lock recess in the bolt. After 

the bolt travels forward about five inches, the lower rear projection 

of the bolt strikes the tips of the accelerator, turning the 

accelerator forward. This unlocks the barrel extension from the 

barrel buffer body group and releases the barrel buffer spring. The 

barrel buffer spring expands, forcing the piston rod forward. 

Since the cross groove in the piston rod engages the notch on the 

barrel extension shank, the barrel extension and barrel are also 

forced forward by the action of the barrel buffer spring. Some of 

the forward motion of the bolt is transmitted to the barrel extension 

through the accelerator. As the accelerator speeds up the barrel 

extension, the accelerator tips slow down the bolt. 

Locking begins 1 1/8 inches before the recoiling groups (bolt, barrel 

extension, and barrel) are fully forward. The breech lock in the 

barrel extension rides up the breech lock cam in the bottom of the 

receiver into the breech lock recess in the bottom of the receiver and 

into the breech lock recess in the bottom of the bolt. This locks 

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the recoiling groups together. The recoiling groups are completely 

locked together three-fourths of an inch before the groups are fully 

forward. 

(4) Firing. As the trigger is pressed down, it pivots on the 

trigger pin, so that the trigger cam on the inside of the backplate 

engages and raises the rear end of the trigger lever which, in turn, 

pivots on the trigger lever pin assembly. This causes the front of 

the trigger lever to press down on the top of the sear stud. The 

sear is forced down until the hooked notch of the firing pin 

extension is disengaged from the sear notch. The firing pin and 

firing pin extension are driven forward by the firing pin spring; the 

striker of the firing pin hits the primer of the cartridge, firing 

the round. 

For automatic firing, the trigger is pressed and held down. The bolt 

latch release must be locked, or held depressed, so that the bolt 

latch will not engage the notches in the top of the bolt. This would 

hold the bolt to the rear, as in single-shot firing. Each time the 

bolt travels forward in counterrecoil, the trigger lever depresses 

the sear releasing the firing pin extension assembly and the firing 

pin, automatically firing the next round when the forward movement of 

the recoiling groups is nearly completed. The gun should fire about 

one-sixteenth of an inch before the recoiling groups are fully 

forward. At the instant of firing, the parts are in battery, i.e., 

the proper position for firing. Only the first round should be fired 

with the parts fully forward. The gun fires automatically as long as 

the trigger and bolt latch are held down, and ammunition is fed into 

the gun. 

(5) Unlocking. At the instant of firing, the bolt is locked to 

the barrel extension and against the rear end of the barrel by the 

breech lock, which is on top of the breech lock cam and in the breech 

lock recess in the bottom of the bolt. 

When the cartridge explodes, the bullet travels out of the barrel; 

the force of the recoil drives the recoiling groups rearward. 

During the first three-fourths of an inch, the recoiling groups are 

locked together. As this movement takes place, the breech lock is 

moved off the breech lock cam stop, allowing the breech lock 

depressors (acting on the breech lock pin) to force the breech lock 

down, out of its recess from the bottom of the bolt. At the 

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end of the first three-fourths of an inch of recoil, the bolt is 

unlocked, allowing it to move to the rear, making it independent of 

the barrel and barrel extension. 

As the recoiling groups move to the rear, the barrel extension causes 

the tips of the accelerator to rotate rearward. The accelerator tips 

strike the lower rear projection of the bolt, accelerating the 

movement of the bolt to the rear. 

The barrel and barrel extension continue to travel to the rear an 

additional three-eighths of an inch, or an approximate total distance 

of 1 1/2 inches, until they are stopped by the barrel buffer 

assembly. During the recoil of the 1 1/8 inches, the barrel buffer 

spring is compressed by the barrel extension shank, since the notch 

on the shank is engaged in the cross groove in the piston rod head. 

The spring is locked in the compressed position by the claws of the 

accelerator, which engage the shoulders of the accelerator, and also 

engage the shoulders of the barrel extension shank. 

After its initial travel of three-fourths of an inch, the bolt 

travels an additional 6 3/8 inches to the rear. This is after it is 

unlocked from the barrel and barrel extension, for a total of 7 1/8 

inches. During this movement, the driving springs are compressed. 

The rearward movement of the bolt is stopped as the bolt strikes the 

buffer plate. Part of the recoil energy of the bolt is stored by the 

driving spring rod assembly, and part is absorbed by the buffer disks 

in the backplate. 

(6) Extracting. The empty case, held by the T-slot, has been 

expanded by the force of the explosion; therefore, it fits snugly in 

the chamber. If the case is withdrawn from the chamber too rapidly, 

it may be torn. To prevent this, and to ensure slow initial 

extraction of the case, the top forward edge of the lock recess in 

the bolt is beveled. As the breech lock is unlocked, the initial 

movement of the bolt away from the barrel and barrel extension is 

gradual. 

The slope of the locking faces facilitates locking and unlocking and 

prevents sticking. The leverage of the accelerator tips on the bolt 

speeds extraction, after it is started, by kicking the bolt to the 

rear to extract the empty case from the chamber. 

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(7) Ejecting. As the bolt starts its forward movement 

(counterrecoil) the extractor lug rides below the extractor switch, 

forcing the extractor assembly further down, until the round is in 

the center of the T-slot. The round, still gripped by the extractor, 

ejects the empty case from the T-slot. The last empty case of an 

ammunition belt is pushed out of the ejector. 

(8) Cocking. When the recoiling groups are fully forward, the top 

of the cocking lever rests on the rear half of the V-slot in the top 

plate bracket. As the bolt moves to the rear, the top of the cocking 

lever is forced forward. The lower end pivots to the rear on the 

cocking lever, which fits through the slot in the firing pin 

extension, forcing the extension to the rear, and compressing the 

firing pin spring against the sear stop pin (accelerator stop). 

As the firing pin extension is pressed to the rear, the hooked notch 

of the extension rides over the sear notch, forcing the sear back up 

after the hooked notch of the firing pin extension has entered the 

sear notch. The pressure of the sear and firing pin springs holds 

the two notches locked together. There is a slight overtravel of the 

firing pin extension in its movement to the rear, to ensure proper 

engagement with the sear. As the bolt starts forward, overtravel is 

taken up and completed when the cocking lever enters the V-slot of 

the top plate bracket, and is cammed towards the rear; pressure on 

the cocking lever is relieved as the bolt starts forward. 

b. Operation. Operation includes loading or unloading the gun, 

clearing the gun, or allowing the bolt to go forward. 

(1) Half-loading and Loading the Gun. Half-loading of an 

automatic weapon occurs when the belt or magazine is inserted and 

is charged, but without the first cartridge actually being inserted 

into the chamber. To half-load the M2, the gunner ensures that the 

bolt is forward and the cover is closed. The assistant gunner 

inserts the double loop end of the ammunition belt in the feedway 

until the first round is engaged by the belt holding pawl. The 

gunner grasps the retracting slide handle with the right hand, palm 

up, and vigorously jerks the bolt to the rear and releases 

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the retracting slide handle. If the bolt latch release lock is 

engaging the bolt latch release, the bolt and retracting slide handle 

will move forward under pressure of the driving spring group, halfloading 

the gun. However, if the bolt latch is up and free of the 

bolt latch release lock, the bolt latch will hold the bolt and 

retracting slide handle to the rear. The retracting slide handle 

must be returned to its most forward position prior to releasing the 

bolt. To complete half-loading, press the bolt latch release, 

allowing the bolt to go forward. 

To fully load the gun, the procedure is the same as in half-loading, 

except it requires the gunner to pull and release the bolt twice. 

(2) Unloading and Clearing the Gun. To unload the gun, the gunner 

unlocks the bolt latch release (if applicable) and raises the cover. 

The assistant gunner lifts the ammunition belt from the feedway. The 

gunner pulls the bolt to the rear and examines the chamber and T-slot 

to ensure they hold no rounds. In darkness, the gunner must feel the 

chamber and T-slot. 

To clear the gun, additional precautions must be taken. After the 

steps above have been accomplished, a wooden block, extending above 

and below the receiver approximately one inch, is inserted in the 

receiver between the bolt and the rear of the barrel. A cleaning rod 

is then inserted in the muzzle end of the barrel, pushed through the 

bore until it can be seen in the receiver, and immediately removed. 

During any temporary stoppage of fire, where it is not necessary to 

unload or clear the gun, the bolt should be latched to the rear to 

prevent accidental firing. 

(3) Precautions During Operation. Ensure that the cover (once 

raised) remains in the raised position. Ensure the barrel remains in 

the gun before allowing the bolt to go forward. If the cover is 

lowered when the bolt is to the rear, the belt feed lever lug will 

not fit into the proper groove in the bolt. Thus, parts may be 

damaged as the bolt goes forward. In the cover assembly, the belt 

feed lever lug is held to the left by the action of the shoulder 

headless pin and spring just above the pivot. 

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If the bolt is allowed to go forward with the barrel out of the gun, 

parts may be damaged when the bolt slams forward. The added weight 

and cushioning effect of the barrel acts as a buffer and protects the 

parts from damage. To allow the bolt to go forward with the barrel 

out of the gun, pull the retracting slide handle all the way to the 

rear, engaging the bolt stud in the notch in the rear of the 

retracting slide. Maintain a steady pressure to the rear on the 

retracting slide handle; press the bolt latch release and allow the 

bolt to ride slowly forward. 

(4) Single Shot Operation. To fire the gun single shot, the bolt 

latch release must be in the up position. The latch engages the 

notches on top of the bolt when the bolt is to the rear after each 

round is fired. When the bolt latch release is depressed the latch 

assembly is raised, allowing the bolt to be driven forward into 

battery. The gun may then be fired by pressing the trigger. When 

the bolt latch release is locked down by the bolt latch release lock 

on the buffer tube sleeve, the gun functions as an automatic weapon. 

4. Components 

The best way to learn the components that comprise a piece of 

equipment is to disassemble that piece of equipment and to study each 

part as it is removed. Therefore, in the following paragraphs, the 

disassembly procedures for the M2 machinegun will be covered. 

It should be noted here that when the operator/unit armorer, or when 

intermediate direct support (IDS) maintenance disassembles the 

weapon, they would clean, inspect and/or repair any discrepancies at 

the time they are found. In this subcourse, however, we will not use 

this procedure. We will cover the disassembly, then the inspection 

and repair procedures, followed by the reassembly procedures. 

a. Disassembly. Disassembly of the M2 machinegun is divided into 

two categories. The first is general disassembly or field stripping; 

the second is detailed disassembly. Field stripping is the removing 

of major groups and assemblies of the gun. This type of disassembly 

is authorized for the operator/unit armorer. Detailed disassembly is 

the disassembly of the major groups and assemblies into 

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the component parts that make up the major group and assembly. 

Detailed disassembly is authorized only at the IDS maintenance level. 

Before beginning any work on this or any other weapon system, first 

clear the weapon. The procedures for clearing the weapon were 

covered in paragraph 3b(2) on page 8 of this task. 

(1) General Disassembly. After the weapon has been cleared, begin 

the disassembly by following the procedures outlined in the following 

paragraphs: 

(a) Barrel Group. 

group (figure 1). 

Turn the cover latch and raise the cover 

FIGURE 1. RAISING THE COVER. 

Grasp the retracting slide handle with the right hand, palm up, and pull 

the recoiling parts to the rear until the lug on the barrel locking 

spring aligns with the 3/8 inch hole in the right sideplate of the 

receiver (just below the feedway exit). The barrel can be turned only 

when the lug is aligned with the 3/8 inch hole. Place the smallest loop 

of a caliber .50 link, or suitable spacer, between the trunnion block 

and the barrel extension (figures 2 and 3 on the following pages). 

10


This holds the barrel locking spring lug aligned with the 3/8 inch 

hole in the right sideplate. 

FIGURE 2. ALIGNING THE BARREL LOCKING 

SPRING LUG WITH THE 3/8 

INCH HOLE. 

Unscrew the barrel from the receiver (figure 4 on the following 

page). Be careful not to damage the threads or barrel locking 

notches when setting the barrel down. Pull back slightly on the 

retracting slide handle and remove the link or spacer from the 

receiver. 

(b) Backplate Group. Ensure that the bolt latch release is in the 

up position, free of the bolt latch release lock. If it is not, push 

down on the bolt latch release and turn the buffer tube sleeve down 

to the right to free it (figure 5 on page 13). The bolt must be 

forward before the backplate is removed. If the bolt is to the rear, 

push down on the bolt latch release and allow the bolt to go forward 

slowly. 

CAUTION 

Care must be taken to prevent the bolt from 

slamming forward with the barrel removed. 

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FIGURE 3. ALIGNING THE BARREL LOCKING 

SPRING LUG USING THE SMALLEST 

LOOP OF THE CALIBER .50 LINK. 

FIGURE 4. REMOVING THE BARREL. 

12


FIGURE 5. BOLT LATCH RELEASE FREE OF THE 

BOLT LATCH RELEASE LOCK. 

Use the retracting slide handle to ease the bolt forward after the 

bolt latch is released. The backplate latch lock and latch are below 

the buffer tube. Pull out on the lock and up on the latch to remove 

the backplate by lifting it straight up (figure 6 on the following 

page). 

(c) Driving Spring Rod Assembly. The inner and outer driving 

springs and driving spring rod are located inside the receiver next 

to the right sideplate (figure 7 on the following page). Push in on 

the head of the driving spring rod and push to the left to remove the 

driving spring rod retaining pin from its seat in the right 

sideplate. Pull the driving assembly to the rear and out of the 

receiver. 

Never attempt to cock the gun while the backplate is off and the 

driving spring assembly is in place. If the backplate is off and the 

driving spring assembly is compressed, the retaining pin on the 

driving spring rod can slip from its seat and cause serious injury to 

anyone behind the gun. 

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FIGURE 6. REMOVING THE BACKPLATE. 

FIGURE 7. DRIVING SPRING ROD ASSEMBLY. 

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(d) Bolt Stud. Grasp the retracting slide handle and give it a 

quick jerk, freeing the bolt from the barrel extension. Align the 

shoulder on the bolt stud with the clearance hole in the bolt slot on 

the right sideplate and remove the bolt stud (figure 8). 

NOTE 

If the bolt latch is accidentally moved all the 

way to the rear, the bolt latch will engage in 

the bolt latch notches in the top of the bolt. 

If this occurs, raise the bolt latch (left of the 

trigger lever) and push the bolt forward to align 

the bolt stud with the clearance hole (figure 9 

on the following page). 

FIGURE 8. REMOVING THE BOLT STUD. 

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FIGURE 9. FREEING THE BOLT. 

(e) Bolt Group. After freeing the bolt, slide it to the rear, 

remove it, and place it on its right side (figure 10). 

FIGURE 10. RECEIVING THE BOLT FROM 

THE RECEIVER. 

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(f) Barrel Buffer and Barrel Extension Groups. Insert a 

pointed instrument through the hole in the lower rear corner of the 

right sideplate and push in on the barrel buffer body lock. With one 

hand in the receiver, push the barrel extension group and barrel 

buffer group to the rear (figure 11) and remove. 

FIGURE 11. REMOVING THE BARREL BUFFER 

GROUP AND BARREL EXTENSION 

GROUP. 

Push the tips of the accelerator forward to separate them (figure 12). 

FIGURE 12. SEPARATING THE GROUPS. 

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(g) Barrel Buffer Assembly. Pull the barrel buffer assembly 

from the rear of the barrel buffer body group (figure 13). The 

barrel buffer assembly will not be disassembled any further. 

FIGURE 13. SEPARATING THE BARREL BUFFER 

ASSEMBLY FROM THE BARREL 

BUFFER BODY GROUP. 

(2) Detailed Disassembly. Once the weapon has been field 

stripped, using the procedures contained in paragraphs 4a(1)(a) 

through 4a(1)(g), on pages 10-18, begin the detailed disassembly of 

the major components and assemblies. These procedures are contained 

in the following paragraphs: 

(a) Bolt Group. First, rotate the extractor upward, (figure 14 

on the following page) and remove it from the bolt, freeing the bolt 

switch. The ejector and ejector spring are not disassembled from the 

extractor. 

Now, lift out the bolt switch and pull out the bolt switch stud 

(figure 15 on the following page). On some models the bolt stud may 

be staked. If staked, do not remove. 

Next, rotate the top of the cocking lever toward the rear of the bolt 

and remove the cocking lever pin; then, lift out the cocking lever. 

The rounded nose of the cocking lever is down and to the rear of the 

bolt (figure 16 on page 20). 

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FIGURE 14. REMOVING THE EXTRACTOR. 

FIGURE 15. REMOVING THE BOLT SWITCH 

AND BOLT SWITCH STUD. 

19


FIGURE 16. REMOVING THE COCKING LEVER 

AND COCKING LEVER PIN. 

Use the thin end of the cocking lever to pry the sear stop, called 

the accelerator stop lock, out of its groove in the bolt, and into 

the center recess (figure 17 on the following page). Turn the bolt 

over and drift the sear stop pin free from engagement with the firing 

pin spring and then shake out the accelerator stop lock (figure 18 on 

the following page). Now, turn the bolt over and lift the sear stop 

and pin from the bolt, then drift out the accelerator stop (figure 19 

on page 22). If the pin does not come out freely, place the thin end 

of the cocking lever under the sear stop, against the pin, and pry it 

out of the bolt. 

20


FIGURE 17. PRYING THE ACCELERATOR STOP 

LOCK INTO THE CENTER RECESS. 

FIGURE 18. DRIFTING THE SEAR STOP PIN. 

21


FIGURE 19. REMOVING THE ACCELERATOR 

STOP LOCK. 

After the accelerator stop lock has been removed, press down on the 

sear and withdraw the sear slide, withdrawing the square end first 

(figure 20 on the following page). To prevent loss of the sear 

spring, insert the thin end of the cocking lever between the coils of 

the sear spring. Lift out the sear and remove the sear spring. 

Leave the spring on the cocking lever (figure 21 on the following 

page). 

Now, raise the front end of the bolt and allow the firing pin 

extension assembly and the firing pin to fall into your hand (figure 

22 on page 24) and separate the firing pin from its extension. 

This completes the detailed disassembly procedures for the bolt 

assembly. Figure 23, on page 24, shows the bolt group disassembled. 

22


FIGURE 20. REMOVING AND REPLACING 

THE SEAR SLIDE. 

FIGURE 21. REMOVING AND REPLACING THE 

SEAR AND SEAR SPRING. 

23


FIGURE 22. REMOVING THE FIRING PIN 

EXTENSION ASSEMBLY AND 

THE FIRING PIN. 

FIGURE 23. BOLT DISASSEMBLED. 

24


(b) Barrel Buffer Body Group. Disassemble the barrel buffer 

group by turning the barrel buffer body group upside down. Pry up on 

the barrel buffer tube lock latch to disengage the latch before 

moving the lock body to the rear. Pry up on the latch end of the 

assembly so that the lug will clear the barrel buffer body. At the 

same time, press down on the front of the lock body to keep it from 

springing out (figure 24). 

FIGURE 24. DISENGAGING THE LATCH. 

25


Turn the accelerator back to push the barrel buffer tube lock 

assembly out of its slot (figure 25). 

In most cases, the barrel buffer body spring lock is staked and will 

not be removed. 

Drift the accelerator pin out and remove the accelerator. 

FIGURE 25. REMOVING THE BARREL BUFFER 

TUBE LOCK ASSEMBLY. 

(c) Barrel Extension Group. First, drift the lockpin out 

and remove the breech lock from the bottom of the barrel extension 

group. The top of the breech lock may have a wide, single-beveled 

edge, or a double-beveled edge. In earlier models, the top may be 

flat (figure 26 on the next page); newer models may have a large 

slot (figure 27 on the following page). Guns currently 

manufactured have the breech lock with the slot on top, for use 

26


with the accelerator stop and lock. When the accelerator stop and 

lock replaces the sear stop and pin, the breech lock with the slot 

will be used. 

FIGURE 26. OLD TYPE BREECH LOCK. 

FIGURE 27. NEW TYPE BREECH LOCK. 

27


(d) Cover Group. With the cover closed, remove the cotter pin 

and drift the cover pin out of the receiver. Unlatch the cover and 

rotate it up and forward to remove the cover from the trunnion block 

(figure 28). Place the cover group top down on a flat, sturdy 

surface, with the latch end to the right and the hinged end toward 

you. 

FIGURE 28. REMOVING THE COVER GROUP. 

28


Remove the belt feed pin, which is a cotter pin. Push the belt feed 

lever to the right, until the toe end of the belt feed lever, which 

engages the slide, is in line with the slot in the cover (figure 29). 

Lift the belt feed lever off its pivot slot. Ensure the shoulder 

headless pin and spring do not fly out. 

FIGURE 29. REMOVING THE BELT FEED LEVER. 

Now, remove the shoulder headless pin and spring from their seat in 

the side of the belt feed lever (figure 30 on the following page). 

Then remove the belt feed slide from either side of the cover group. 

Drift the belt feed pawl pin out, maintaining pressure on the belt 

feed pawl to prevent the spring from flying out (figure 31 on the 

following page). 

29


FIGURE 30. REMOVING THE SHOULDER HEADLESS 

PIN AND SPRING. 

FIGURE 31. REMOVING THE BELT FEED 

PAWL PIN. 

30


Slowly release the pressure, and remove the belt feed pawl and arm 

(figure 32). 

Disengage the belt feed pawl arm (figure 33). 

FIGURE 32. REMOVING THE BELT FEED 

PAWL AND ARM. 

FIGURE 33. DISENGAGING THE BELT 

FEED PAWL ARM. 

31


Now, remove the belt feed pawl spring. Then, pry the hooked end of 

the spring out of its groove in the cover, and shift it to the left 

until it rests on the cover extractor spring. Press down on the 

cover latch spring, and slide it away from the cover latch. Make 

sure that it rides on top of the cover extractor spring. When the 

enlarged hole in the spring meshes with the cover latch spring stud, 

remove the spring from its stud (figure 34). 

FIGURE 34. REMOVING THE COVER LATCH SPRING. 

Press down on the cover extractor spring and pry the end of the 

spring out of its recess in the cover extractor cam (figure 35 on the 

following page). This spring, if not handled carefully, can cause 

injury. Disengage the opposite end of the spring from the cover 

extractor spring stud. 

This completes the detailed disassembly procedures for the cover 

group. In the next paragraphs, the detailed disassembly procedures 

for the receiver group will be discussed. 

32


FIGURE 35. REMOVING THE COVER EXTRACTOR 

SPRING. 

(e) Receiver Group. To disassemble the receiver group, first, 

press down on the spring belt holding pawl and withdraw the belt 

holding pawl pin to the rear; use care not to lose the two springs. 

FIGURE 36. BELT HOLDING PAWL ASSEMBLY. 

33


The split belt holding pawl assembly includes a left-hand and righthand 

belt holding pawl, connected by a belt holding pawl sleeve; two 

belt holding pawl springs are used (figure 36 on the previous page). 

Guns of earlier manufacture use a single belt holding pawl, adapted 

for either one or two springs (figure 37). 

N o w , w i t h d r a w t h e b e l t h o l d i n g p a w l p i n f r o m t h e 

r i g h t s i d e o f t h e r e c e i v e r . R e m o v e t h e c a r t r i d g e 

FIGURE 37. RECEIVER GROUP WITH OLD 

TYPE BELT FEED PAWL. 

34


stop assembly (or rear cartridge stop and link stripper on guns of 

earlier manufacture), and front cartridge stop, from the right side 

of the receiver (figure 38). 

Release the hinged lock from the left sideplate; turn the pin 

clockwise, and withdraw the pin to the left. Remove the trigger lever 

from inside the receiver. Guns of earlier manufacture may have a 

FIGURE 38. CARTRIDGE STOP ASSEMBLY, FRONT 

CARTRIDGE STOP, AND BELT 

HOLDING PAWL PIN. 

35


trigger lever pin assembly without the hinged lock. In this case, 

lift the lock of the pin out of the small hole in the left sideplate 

and rotate the lock end downward 90 degrees until it is just forward 

of a vertical position. Withdraw the pin to the left (figure 39). 

This completes the detailed disassembly procedures. 

FIGURE 39. REMOVING THE TRIGGER LEVER PIN. 

36


5. Tripod Mount, M3 

The M3 mount is the standard ground mount of the caliber .50 

machinegun (figure 40 on the following page). It is a folding tripod 

with three telescopic, tubular legs, connected at the tripod head. 

Each leg ends in a metal shoe, which can be stamped into the ground 

for greater stability. The two trail legs are joined together by the 

traversing bar. The traversing bar serves as a support for the 

traversing and elevating mechanism, which in turn supports the rear 

of the gun. The tripod head furnishes a front support for the 

mounted gun which is further supported by the short front leg. When 

the tripod is emplaced on flat terrain, with all extensions closed, 

the adjustable front leg should form an angle of about 60 degrees 

with the ground. This places the gun on a low mount, about 12 inches 

above the ground. To raise the tripod farther off the ground, extend 

the telescopic front and trail legs (enough to keep the tripod level 

and maintain the stability of the mount). 

a. General Data. The weight of the pintle and traversing and 

elevating mechanism are considered as part of the total weight of the 

tripod mount, M3 (44 lbs). 

b. Front Leg and Leg Extensions. 

(1) Front Leg. To adjust the front leg, turn the front leg clamp 

screw handle counterclockwise to loosen the front leg clamp screw 

nut. Adjust the leg to the desired angle, and tighten the front leg 

clamp. 

(2) Leg Extensions. To extend any of the tripod legs, unscrew 

the leg clamping handle; press down on the indexing-lever, and extend 

the leg to the desired length. Align the stud on the indexing lever 

with one of the holes in the tripod leg extension. Release the 

pressure on the indexing lever, allowing the stud to fit the desired 

hole. 

37


FIGURE 40. M3 TRIPOD MOUNT. 

38


c. Traversing and Elevating Mechanism. 

(1) The Traversing Mechanism. Consists of a traversing bar, 

slide, and screw assembly. The traversing bar, graduated in five mil 

increments, fits between the trail legs of the tripod. The 

traversing slide and screw assembly are clamped in place on the 

traversing bar by the traversing slide lock lever. When the 

traversing slide is locked to the traversing bar, the traversing 

handwheel should be centered. The traversing slide is properly 

mounted when the lock lever is to the rear and the traversing 

handwheel is positioned to the left. 

To make changes in direction, loosen the traversing slide lock lever 

and move the slide along the traversing bar. This permits traverse 

of 400 mils left or right of the zero index in the center of the 

traversing bar. Readings on the traversing bar are taken from the 

left side of the traversing slide. For changes of 50 mils or less in 

deflection, turn the traversing handwheel of the screw assembly. 

This allows a traverse of 50 mils left or right of center. One click 

in the traversing handwheel signifies one mil change in direction. 

(2) The Elevating Mechanism. Consists of an upper and lower 

elevating screw, and is connected to the gun by inserting the quick 

release pin assembly through the holes in the upper elevating screw 

yoke and the rear mounting lugs of the receiver. A scale, graduated 

in mils, is fitted to the upper screw to indicate elevation. This 

scale is marked to show 250 mils in depression and 100 mils in 

elevation from the zero setting. 

The elevating handwheel is graduated in one mil increments up to 50 

mils, and is fastened to the elevating screw by a screw lock. This 

synchronizes the handwheel graduations with those on the upper 

elevating screw. A spring actuated index device produces a clicking 

sound when the handwheel is turned. Each click equals one mil change 

in elevation. The handwheel is turned clockwise to depress the 

barrel and counterclockwise to elevate. Figure 41, on the following 

page, shows details of the elevating mechanism. 

39


FIGURE 41. ELEVATING MECHANISM. 

40


d. Pintle. The gun is connected to the tripod mount, M3, by a 

pintle. This pintle is semipermanently attached to the machinegun by 

a pintle bolt through the front mounting hole in the receiver. The 

tapered stem of the pintle seats in the tripod head, and is held 

secure by a pintle lock and spring. To release the pintle, raise the 

pintle lock, releasing the cam. 

6. Conclusion 

This concludes this task dealing with the components and operation of 

the M2 caliber .50 machinegun. In the next task, we will cover the 

inspection and maintenance procedures employed by unit and 

intermediate direct support (IDS) levels of maintenance to keep this 

weapon operating. 

41


LESSON 1 

THE COMPONENTS, OPERATION, INSPECTION, AND 

MAINTENANCE PROCEDURES FOR THE M2 MACHINEGUN 

TASK 2. 

Describe the inspection and maintenance procedures for the 


CONDITIONS 

Within a self-study environment and given the subcourse text, without 

assistance. 

STANDARDS 

Within three hours 

REFERENCES 

No supplementary references are needed for this task. 

1. Introduction 

In task 1, the importance of the operation, and the components of the 

Browning caliber .50 M2 machinegun HB were discussed. This 

information was presented, because an understanding of the operation 

and components is essential in gaining a knowledge of the inspection 

and maintenance procedures. 

The inspection and maintenance procedures are the purpose of this 

task. After reading this task, the student should have a thorough 

understanding of the practices and procedures used to inspect and 

maintain the M2 machinegun and the M3 tripod mount. 

2. Inspection and Maintenance Procedures 

In the paragraphs that follow, the procedures to be used when 

inspecting and repairing the M2 machinegun and the M3 tripod 

mount will be discussed. The inspection and repair procedures 

for this particular task will be divided into two categories. 

First, the inspection and repair procedures performed by the user 

and the unit armorer, and second those inspection and repair 

42


procedures used by intermediate direct support (IDS) maintenance. 

a. Unit Inspection and Repair Procedures. The weapon should be 

inspected by the user every day to ensure its serviceability. These 

inspection procedures are known as the preventive maintenance checks 

and services (PMCS). These inspection procedures should be performed 

before and during the disassembly of the weapon. Prior to beginning 

any work on this or any other weapon, first, ensure that the weapon 

is clear of ammunition. The procedures for clearing the weapon were 

covered in paragraph 3b(2) on page 8 of task 1. Throughout these 

paragraphs, unit level maintenance personnel are directed to effect 

corrective action either through repair and/or replacement of 

defective components. Before beginning any repair or replacement 

procedures, first consult the maintenance allocation chart (MAC) in 

Appendix B, TM 9-1005-213-25, to ensure that your level of 

maintenance is authorized to repair or replace the defective 

components. If your level of maintenance is not authorized to make 

the repairs, the item must be sent to IDS maintenance for repair. 

(1) Preventive Maintenance Checks and Services. First, check the 

functioning of the weapon by using dummy ammunition. Once the 

functioning of the weapon has been tested, inspect the components 

and/or assemblies for any obvious defects such as nicks, burrs, rust 

corrosion, loose or missing rivets, screws, nuts and washers. Repair 

or replace any components found to be defective, provided that your 

level of maintenance is authorized to perform this function. 

(a) Barrel Assembly/Group. Inspect the bore with a barrel 

reflector for rust, powder fouling, and obstructions. Check the 

barrel threads and locking notches for serviceability. Check the 

components of the barrel carrier assembly for serviceability. The 

retaining pin should be staked in the knob of the carrier assembly. 

The handle group should secure the carrier assembly firmly to the 

barrel assembly. 

(b) Back Plate Assembly/Group. Ensure that the buffer tube 

sleeve rotates freely and the lock engages the bolt latch release. 

Operate the trigger to ensure that it functions properly. 

43


Ensure correct adjustment of the machine thread plug. Also ensure 

that the solenoid is secured with corrosion resisting wire and that 

the solenoid cable is not damaged or broken. 

(c) Bolt Group and Rod Assembly. Inspect the firing pin tunnel 

in the bolt for powder fouling and foreign matter. 

(d) Barrel Buffer Group. Inspect the buffer body lock for 

deformation and retention. The lock must be securely staked to the 

buffer body. 

(e) Barrel Extension Group. Check the barrel locking spring to 

ensure that it puts tension on the lock to keep the barrel extension 

group securely mounted. 

(f) Retracting Slide Assembly. Inspect the retracting slide 

assembly for loose studs, loose handle or loose lever. Check for a 

bent slide lever and whether the spring maintains the handle in an 

upright position. Ensure the installation of locking wire in two 

places secures the retracting slide assembly mounting screws. 

(g) M10 Manual Charger. The inspection and repair procedures 

for the M10 manual charger will be presented in this text. However, 

it should be noted that the M10 manual charger is found only on the 

M48 version of the M2 machinegun. Inspect the charger cable assembly 

for broken or frayed strands. The charger should be secured to the 

receiver with screws which accommodate corrosion resisting wire. 

(h) Cover Group. Manually operate the feed mechanism to ensure 

freedom of movement. 

(i) Receiver Group. Check the trunnion block for cracks in the 

feedway. Check the receiver group for loose rivets in the trunnion 

block area. Inspect the adjustable trigger bar nut spring for broken 

prongs. Evacuate the receiver group to IDS maintenance if riveted 

components are loose or if weld failure is detected. 

(j) M3 Tripod Mount. First, inspect the traversing slide 

lock lever for proper function. Check the traversing and 

elevating mechanism assembly for smoothness of operation and 

broken or missing components. Replace those components found 

44


to be unserviceable. Remember, consult the MAC to ensure that it is 

within your maintenance capabilities to replace the defective parts. 

If it is not within your maintenance capabilities, send the defective 

item to IDS maintenance. 

Check the functioning of the legs and sleeve lock latch. Inspect all 

components for dents, cracks, or distortion. Check the clamping 

handle and round nut for retention on the legs and check for wear or 

distortion of the threads. Check the rear legs for full extension. 

The rear legs should be forced slightly apart by the traversing bar 

assembly when in the firing position. Check machine bolt 5139973 and 

the slotted nut for damaged threads or burrs. Finally, check the 

head for evidence of cracks or burrs. Again, repair by replacing 

defective components. 

(2) Cleaning. In the paragraphs that follow, the cleaning 

procedures used by unit maintenance (user and unit armorer) before, 

during, and after firing and under unusual climatic conditions will 

be discussed. 

(a) Care and Cleaning Before, During, and After Firing. Before 

firing, when the situation permits, take the following steps to 

ensure efficient functioning of the machinegun: 

Step 1. 

assemblies. 

Disassemble the gun into its major groups or 

Step 2. Clean the bore and the chamber, but do not oil them. 

Step 3. Clean all the metal parts thoroughly and apply a light 

coat of oil to all metal parts which do not come in contact with the 

ammunition. 

Step 4. To ensure complete removal of powder residue and 

primer fouling from the bore of the machinegun barrel, the bore 

should be cleaned at least once a day, for at least three consecutive 

days after firing. The bore sweats out this fouling or residue, and 

cleaning must be repeated until there is no further evidence of 

sweating. 

(b) Care and Cleaning Under Unusual Climatic Conditions. 

Extreme cold, dry, hot, and tropical climates affect the gun and its 

functioning. Care should be taken under these climatic conditions to 

45


ensure that the gun is cleaned daily with the prescribed lubricants 

and protected from the elements by some sort of cover if possible. 

Further information on the care and cleaning of the M2 machinegun 

under unusual climatic conditions can be found in TM 9-1005-213-10. 

(3) Inspection and Repair. In the paragraphs that follow, the 

inspection and repair procedures used by unit maintenance for the 

groups/assemblies of the M2 machinegun will be discussed. 

(a) Machinegun. Visually inspect the components for wear, 

cracks, dents, and damage. Springs must be free of rust, corrosion, 

and deformation. Make certain all parts are properly installed and 

in working condition. 

Repair the exterior of the machinegun by removing rough edges. 

Remove all traces of rust or scored areas from the finished surfaces 

with crocus cloth moistened lightly with oil. 

(b) Barrel Assembly. Check for bulges, burrs, corrosion, and 

rust. Inspect the chamber and bore with the barrel reflector for 

pitting and rust. Replace the barrel assembly if it is found to be 

unserviceable. 

(c) Back Plate Assembly/Group. Check the latch and latch lock 

for missing or broken lock pins and replace as necessary. Inspect 

the machine thread plug for damaged threads and the slot for burrs. 

Inspect the helical compression spring (machine thread plug) for 

corrosion, weakness, or distortion. Notify IDS maintenance if the 

spring is unserviceable. Inspect the buffer disks for frayed or 

broken conditions, and for the correct count to ensure that there are 

22 buffer disks. Replace any disk(s) found to be unserviceable. 

Inspect the trigger for bent or broken conditions. If trigger 

6008918 is unserviceable, notify IDS maintenance. Examine the 

solenoid trigger and replace if found to be unserviceable. Examine 

the electrical solenoid for looseness and damage. Check the riveted 

clip assembly and the clamp assembly for damage. Replace any of the 

above noted items found to be defective. 

(d) Bolt Group and Rod Assembly. Inspect the bolt group and rod assembly 

components for damage. Replace only authorized parts as required. Inspect 

46


the driving spring rod assembly to ensure that it is not bent. 

Replace if necessary. Inspect the bolt switch for roughness or 

burrs. If found to be unserviceable, replace. Inspect the bolt 

assembly to see that there are no sharp corners on any surface. 

Replace any parts found to be unserviceable. Check for the proper 

usage and compatibility of parts when replacing unserviceable 

components. 

(e) Barrel Buffer Group. Inspect the accelerator pin assembly 

for burrs or rust and for a broken or missing spring. Replace any 

components found to be unserviceable. Be sure to check for proper 


components. Ensure that the buffer assembly does not contain oil. 

Oil is used only in aircraft-type weapons. 

(f) Barrel Extension Group. Inspect the breech lock pin 

assembly for burrs or rusting. Inspect the barrel locking spring for 

firm retention in the groove and for wear, fracture, and burrs, 

especially on the nose. Replace any components found to be 


(g) Retracting Slide Assembly. Inspect all parts for damage or 

a broken condition. If the damaged parts are not components unit 

maintenance are authorized to replace, notify IDS maintenance. 

(h) M10 Manual Charger. Examine the cable for broken or frayed 

strands, and replace if found to be unserviceable. Replace all 

spring pins, screws, and washers removed during disassembly, provided 

they are damaged or worn. If any of the components are 

unserviceable, replace the entire charger assembly. 

(i) Cover Group. Inspect the belt feed lever for fracture, 

deformation, and free movement on the pivot stud. If the belt 

feed lever is bent or broken, this would cause the weapon to fail 

to chamber a round, thereby rendering it useless to the user. 

Inspect the lugs on the ends for wear and for a missing headless 

shoulder pin. Inspect the belt feed slide assembly for burrs. 

The protruding pin, when assembled, should be flush. Inspect the 

belt feed pawl assembly for burrs, bent or missing pins. Replace 

any components found to be unserviceable. If the belt feed pawl 

arm is bent or broken, notify IDS maintenance. If the 

47


cover group does not lock securely, notify IDS maintenance. 

(j) Receiver Group. Inspect the trigger level pin assembly for 

burrs or a broken lock. Inspect the trigger lever for deformation or 

burrs on the camming surfaces. Check the headspace and timing when 

the gun is assembled. If the headspace and timing cannot be 

adjusted, notify IDS maintenance. Check the cartridge stops and link 

stripper for correct position and condition. If unserviceable, 

notify IDS maintenance. Inspect the belt holding pawl assembly for 

burrs, wear and dirt. Check the belt-holding pawl pins to see that 

they fit snugly and are not broken. Replace any components found to 

be unserviceable. Check the components of the electrical solenoid 

assembly. If the cable assembly and corrosion resisting wire are 

unserviceable, replace them. Replace the solenoid if it is 


(k) M3 Tripod Mount. Visually inspect the components for wear, 

cracks, dents, and damage. Springs must be free of rust, corrosion, 

and deformation. Make certain all parts are properly installed and 

in working condition. Remove burrs, rough edges, and all traces of 

rust from finished or functional surfaces with a crocus cloth 

moistened lightly with oil. 

Inspect for smoothness of traversing and elevating screws. Check the 

helical torsion spring and lever for clamping action on the 

traversing bar assembly. Check the quick release pin and chain 

assembly for burrs and damage. 

Inspect the legs for distortion, dents, and burrs. Check the 

telescoping function of the legs and leg sections. Check the 

adjustment of the traversing bar assembly when the legs and leg 

sections are extended. They must fit flush with the side of the 

tripod head. Check the functioning of the lever assembly, tension of 

the spring, and for a loose pin. Inspect the spades of the legs and 

leg sections for cracks at welds, and for being bent or damaged. 

Check the condition of the pins and pin holes in the tubing of the 

lower leg sections. Check the functioning of the leg clamping handle 

when the legs and leg sections are extended. Also, check for 

looseness in the handle and for burred or damaged threads. Check the 

lower leg sections for rust and dirt. Check the components of the 

48


traversing bar assembly for distortion, dents, looseness, wear, and 

burrs. Replace only authorized components if unserviceable. 

When the tripod mount is placed in the firing position, the legs must 

be forced slightly apart and must contact the side of the head to 

ensure rigidity of the mount. If looseness is encountered, adjust 

the traversing bar assembly, as required. 

Check the bolts and nuts for damaged threads and burrs. Check the 

pintle and bearing for looseness and burrs. Check the tripod head 

for cracks and burrs. Check the lock assembly for looseness and 

burrs. Check the locking action of the lock assembly. Inspect the 

serrated plates for gouges or other damage. Check the clamping 

action function of nut 5139964 on the serrated plates and for any 

loose play when locked. 

(4) Headspace and Timing. Headspace is the distance between the 

face of the bolt and the base of the cartridge case when it is fully 

seated in the chamber. Headspace adjustment is correct when the 

following conditions are met: the recoiling groups are fully forward 

and there is no independent rearward movement between the bolt, 

barrel, and barrel extension. An improper headspace adjustment can 

cause the gun to function improperly. It may also result in damage 

to parts and/or injury to personnel. 

Headspace is checked and set prior to firing. Other instances 

include: when the gun is disassembled, when the barrel or any major 

group or assembly within the receiver is replaced, and when there is 

doubt that the correct headspace is set. 

The headspace and timing gage consists of a headspace gage and two 

timing gages. These gages provide an accurate means of checking the 

adjustment of headspace and timing. 

(a) Headspace Adjustment with the Gage. With the gage, the 

distance between the face of the bolt and the chamber end of the 

barrel can accurately be determined by the following procedures: 

Raise the cover and retract the recoiling parts following the procedures 

contained in paragraph 3b(2) on page 8 of task 1. Next, screw the 

barrel 

49


all the way into the barrel extension, then unscrew the barrel two 

notches. 

Cock the gun by pulling the retracting slide handle all the way to 

the rear, then return it to its most forward position. Press the 

bolt latch release and allow the bolt to go forward. Be careful not 

to depress the trigger since this will cause the firing pin to be 

released. If the firing pin is forward, the gage cannot be inserted 

into the T-slot far enough to give an accurate determination. Never 

release the firing pin with the gage in the T-slot as this could 

damage to the firing pin and the gage. 

Now pull the retracting slide handle back until the barrel extension 

is about one-sixteenth of an inch from the trunnion block. This will 

ensure that the locking surfaces of the breech lock and the bolt are 

in proper contact. This prevents the driving spring group and the 

weight of the parts from giving a false determination. 

First, insert the GO end of the headspace gage in the T-slot, between 

the face of the bolt and the rear end of the barrel. If the GO end 

of the gage enters freely down to the center ring of the gage, then 

attempt to insert the NO GO end of the gage. If the GO end enters 

and the NO GO does not enter, correct headspace is set. 

If the GO end of the gage does not enter freely, the headspace is too 

tight. When this condition exists, the barrel must be unscrewed one 

click (notch) at a time, checking with the gage after each click, 

until the GO end of the gage enters freely. To complete the 

adjustment, attempt to insert the NO-GO end of the gage; if it does 

not enter, the correct headspace is set. Remember to screw or 

unscrew the barrel into the barrel extension; the lug on the barrel 

locking spring must be aligned with the 3/8 inch hole in the right 

side plate. 

If the NO GO end of the gage enters the T-slot, the headspace is too 

loose. The barrel must be screwed into the barrel extension one 

click at a time, checking with the gage after each click, until the 

GO end enters and the NO-GO end does not enter. After the headspace 

has been checked and adjusted, remove the gage. 

50


(b) Timing. Timing is the adjustment of the weapon so that 

firing takes place when the recoiling parts of the weapon are between 

.020 and .116 inches out of battery to prevent contact between the 

front end of the barrel extension and the trunnion block. Timing is 

correctly set when the following conditions are met: the recoiling 

parts are locked together, firing takes place just before the parts 

are in battery (fully forward), and when the gun fires on the FIRE 

gage, but does not fire on the NO FIRE gage. Timing must be checked 

and/or set each time headspace is set, or whenever timing is 

questionable. 

(c) Checking and/or Setting Timing. Ensure that the gun has 

the correct headspace adjustment. Cock the gun; pull the retracting 

slide handle all the way to the rear, and return it to its most 

forward position. Press the bolt latch release and allow the bolt to 

go forward. Do not depress the trigger. Raise the extractor and 

pull the retracting slide handle back until the front end of the 

barrel extension is about one-fourth of an inch from the trunnion 

block. 

Insert the NO FIRE timing gage between the barrel extension and the 

trunnion block, placing the beveled edge of the gage on the barrel 

notches. Let the barrel extension close slowly on the gage. 

Depress the trigger firmly, attempting to release the firing pin. 

The firing pin should not release. If the firing pin does release, 

the gun is timed to fire too early. To correct for this, pull the 

retracting slide handle to the rear, allow the bolt to go forward. 

Insert the fire gage, remove the backplate and screw the timing 

adjustment nut to the left until it rests on the trigger lever. 

Press up firmly on the trigger lever and attempt to fire. Rotate the 

timing adjustment nut to the right, one notch at a time, each time 

pressing up firmly on the trigger lever, and attempt to fire the 

weapon. When the firing pin is released, turn the timing adjustment 

nut two additional notches to the right and replace the backplate. 

CAUTION 

Do not attempt to cock the gun with the backplate 

off. 

51


Recock the weapon and allow the bolt to go forward. Insert the NO 

FIRE gage between the trunnion block and the barrel extension. 

Attempt to fire the weapon by depressing the trigger. The weapon 

should not fire. If the weapon does fire, a mechanical defect exists 

and the proper troubleshooting and repair procedures should be used 

to locate and correct the cause of the malfunction. 

Replace the NO FIRE gage with the FIRE gage and attempt to fire the 

weapon. The weapon should fire. When all of the above procedures 

have been completed, the weapon is correctly timed. 

This completes the inspection and repair procedures used at unit 

level maintenance. Additional procedures and information can be 

found in FM 23-65 and TM 9-1005-213-25. 

b. IDS Inspection and Repair Procedures. In the paragraphs that 

follow, the inspection and repair procedures used by IDS maintenance 

personnel will be discussed. Basically, IDS maintenance will perform 

the same inspection that unit level maintenance personnel perform. 

The only difference is that IDS will go into more detail. It should 

be noted that the actual inspection would be performed as the weapon 

is disassembled and any parts found to be defective would either be 

repaired or replaced at that time. 

(1) Machinegun. Visually inspect the components for wear, cracks, 

dents, and damage. Springs must be free of rust, corrosion, and 

deformation. Make certain all parts are properly installed and in 

working condition. 

Repair the exterior of the machinegun by removing rough edges. 

Remove all traces of rust or scored areas from the finished surfaces 

with crocus cloth moistened lightly with oil. 

(2) Barrel Assembly. Check for bulges, burrs, corrosion, and 

rust. Inspect the chamber and bore with the barrel reflector 

for pitting and rust, replace the barrel assembly if it is found 

to be unserviceable. If the barrel installed on the weapon is 

unlined, use barrel erosion gage 7319900 and check the barrel 

erosion. If the barrel is lined, use barrel erosion gage M6A1 

to check the barrel erosion. If the weapon is being sent 

52


overseas, barrel erosion cannot exceed the thirteenth graduation on 

the gage. If the weapon is to be used by troops in the United 

States, barrel erosion cannot exceed the twentieth graduation as 

indicated on the barrel erosion gage. Reject the barrel assembly if 

the barrel is worn enough to affect the sharpness of lands. Make 

sure serrations are well defined so as to retain the barrel assembly 

setting by the locking spring. The barrel should not be able to be 

rotated after it is attached to the receiver. 

(3) Backplate Assembly/Group. Check the latch and latch lock for 

missing or broken lock pins and replace as necessary. Inspect the 

machine thread plug for damaged threads and the slot for burrs. The 

machine thread plug should be tight. Headless shoulder pin 5152839 

will be in the locking notch in the buffer tube. The buffer plate 

should protrude approximately 3/16 of an inch from the front of the 

backplate. Inspect the helical compression spring (machine thread 

plug) for corrosion, weakness, or distortion. Replace the spring if 

it is unserviceable. 

Inspect the buffer disks for frayed or broken condition, and for 

correct quantity. There should be 22 buffer disks. Replace any 

disk(s) found to be unserviceable. Inspect the trigger for bent or 

broken condition. If the weapon is equipped with a solenoid and 

electrical trigger, inspect them for damage or unserviceable 

condition and proper retention. If an unserviceable condition 

exists, repair or replace the necessary components. Examine the 

electrical solenoid for looseness and damage. Check the riveted clip 

assembly and the clamp assembly for damage. Replace any of the above 

noted items found to be defective. The backplate assembly should fit 

firmly on the receiver group, but freely enough to be removed by hand. 

(4) Bolt Group and Rod Assembly. Inspect the bolt group and 

rod assembly components for damage. Replace only authorized 

parts as required. Inspect the driving spring rod assembly to 

ensure that it is not bent and replace if necessary. Inspect 

the bolt switch for roughness or burrs. If found to be 

unserviceable, replace. Inspect the bolt assembly to see that 

there are no sharp corners on any surface. Replace any parts 

found to be unserviceable. Check for the proper usage and 

53


compatibility of parts when replacing unserviceable components. 

Check the clearance of the bolt group with the sideplate. The recoil 

plate should be flush with the face of the bolt assembly. The 

trigger lever should not drag on the bolt group when the trigger is 

depressed. The angle on the mating surface that engages the firing 

pin extension must be sharp, without a feather edge. The stud must 

be staked in three places. 

Measure the firing pin protrusion using gage 7799739. The minimum 

allowable protrusion of the firing pin is 0.073 inch, while the 

maximum allowable firing pin protrusion is 0.080 inch. Use NO-GO 

plug gage 7458406 and measure the firing pin hole. The firing pin 

hole must not exceed 0.084 inch in diameter. If the NO-GO gage 

enters the firing pin hole all the way, the bolt group should be 

rejected. Elongation of the firing pin hole is also cause for 

rejection. Inspect the firing pin and extension for wear, damage, 

rust, or corrosion. The sear engaging notch on the firing pin 

extension should have a black or dull gray finish, and the angle must 

be sharp without a feathered edge. 

(5) Barrel Buffer Group. Inspect the accelerator pin assembly for 

burrs or rust and for a broken or missing spring. Replace any 

components found to be unserviceable. Be sure to check for proper 


components. 

NOTE 

Ensure that the buffer assembly does not contain 

oil. Oil is used only in aircraft-type weapons. 

The overall length of the buffer assembly (rear face of the tube to 

the forward inside face of the engaging notch) must be between 6.086 

and 6.117 inches. Use oil buffer rod gage 7160900 to make this 

measurement. 

The breech lock depressors may have vertical movement which 

does not exceed 3/32 of an inch and lateral movement which 

does not exceed 1/16 of an inch, measured at the tips. 

Longitudinal movement must not exceed .005 inch. The buffer 

body lock must not be overstaked. Staking or swaging to 

54


secure or limit the movement of the breech lock depressors in their 

recesses in the buffer body is not permitted. Marks derived from 

previous unauthorized staking or swaging of the buffer bodies will be 

acceptable if the function is not affected. The guide must be 

sufficiently staked and free of damage. Do not put oil in the buffer 

assembly; oil is used in aircraft-type guns only. 

(6) Barrel Extension Group. Inspect the breech lock pin assembly 

for burrs or rusting. Inspect the barrel locking spring for firm 

retention in the groove and for wear, fracture, and burrs, especially 

on the nose. Replace any components found to be unserviceable. 

(7) Retracting Slide Assembly. Inspect all parts for damage or a 

broken condition. 

(8) M10 Manual Charger. Examine the cable for broken or frayed 

strands, and replace if found to be unserviceable. Replace all 

spring pins, screws, and washers removed during disassembly, provided 

they are damaged or worn. If any of the components are 

unserviceable, replace the entire charger assembly. 

(9) Cover Group. Inspect the belt feed lever for fracture, 

deformation, and free movement on the pivot stud. Inspect the lugs 

on the ends for wear and for a missing headless shoulder pin. 

Inspect the belt feed slide assembly for burrs. The protruding pin, 

when assembled, should be flush. Inspect the belt feed pawl assembly 

for burrs, bent surfaces, and missing pins. Replace any components 

found to be unserviceable. If the belt feed pawl arm is bent or 

broken, replace it. If the cover group does not lock securely, 

replace the cover group latch assembly. Measure the cover latch and 

notch clearance. If the weapon is destined for overseas service, the 

measurement between the cover latch and notch should be a maximum of 

0.010 inch. If the weapon is to be used in the United States, the 

measurement should be 0.015 inch. If either of these two 

measurements is not indicated when the measurement is taken, replace 

the cover latch. 

(10) Receiver Group. Inspect the trigger level pin assembly for 

burrs or a broken lock. Inspect the trigger lever for deformation 

or burrs on the camming surfaces. Check the headspace and 

timing when the gun is assembled. If the headspace and 

55


timing cannot be adjusted, troubleshoot the weapon to identify and 

locate the malfunction, then perform the corrective action. Check 

the cartridge stops and link stripper for correct position and 

condition. If they are unserviceable, replace them. 

Inspect the belt-holding pawl assembly for burrs, wear and dirt. 

Check the belt-holding pawl pins to see that they fit snugly and are 

not broken. Replace any components found to be unserviceable. Check 

the components of the electrical solenoid assembly. If the cable 

assembly and corrosion resisting wire are unserviceable, replace 

them. Replace the solenoid if it is unserviceable. 

Inspect the trunnion blocks for cracks, wear, rust and corrosion. If 

the trunnion blocks are rusted or corroded, remove the corrosion, 

treat the metal with a corrosion preventive compound and refinish the 

trunnion blocks. If the trunnion blocks are cracked or worn, replace 

them. Check the pawl and helical compression spring. The spring 

must not bind in the trunnion block and must hold the cover open in 

positions of quarter, half, and full open. 

Now inspect the top and bottom plates for loose rivets, bends, and 

other damage. Also check the bottom plate for damage at the mounting 

holes and the bolt latch. The following inspection criteria will 

apply in the inspection for loose rivets: if the .005 inch leaf of 

the feeler gage penetrates to the depth of the rivets at any point in 

the riveted area, the weapon will be turned in for overhaul and a new 

weapon drawn from stock. 

Use a feeler gage and check the trigger lever clearance. Refer to 

figure 42 on the following page; retract the bolt group 1 and 1/2 

inches. Insert the feeler gage between the top of the bolt and the 

bottom of the trigger lever. The clearance between the trigger lever 

and the bolt should be a minimum of 0.005 inch. If the trigger lever 

clearance is not within tolerance, rotate the adjusting knob either 

clockwise or counterclockwise and bring the trigger lever within the 

proper clearance. 

56


FIGURE 42. MEASURING TRIGGER LEVER 

CLEARANCE. 

Now check the adjustment of the breech lock cam. This is done by 

inserting a feeler gage between the cam and the bottom of the 

receiver group as shown in figure 43, on the following page. The 

adjustment should be between 0.001 inch and a maximum of 0.008 inch. 

If the adjustment is not within these limits, remove the cotter pin 

from the castle nut on the cam adjusting screw. Then rotate the 

screw either right or left to bring the cam adjustment to the proper 

tolerances. 

Finally, inspect the rear sight assembly. Ensure that only 

acceptable types of rear sights are used. Observe the clicking 

action of the plungers and springs; flat spring 7265577 must hold the 

leaf at a 90 degree angle without excessive play in the leaf 

assembly. Figure 44, on the following page, shows only those rear 

sight assemblies that are acceptable. 

57


FIGURE 43. MEASURING CAM CLEARANCE. 

FIGURE 44. ACCEPTABLE REAR SIGHTS. 

58


(11) M3 Tripod Mount. First, inspect all pins, springs, and 

handwheels for proper functioning. Now measure the distance between 

the sleeves and the collar. This distance should not be less than 

1/2 inch or more than 3/4 inch before locking traversing bar assembly 

to the right rear leg. Now measure the distance between the pintle 

shoulder and the tripod head. The distance should be a minimum of 

0.003 inch. 

When inspecting the traversing and elevating mechanism assembly, 

ensure that the pointer and designation plate on the upper elevating 

screw coincide with the 0 reading. The dial pointer will be staked 

to the click ring in three places. 

Now inspect the legs and tripod head group. First, the serrations 

must be clear when the legs are being adjusted and in proper 

alignment to ensure an even spread of the legs when they are clamped. 

Ensure that the sleeve bearing is sufficiently staked at each end of 

the screw slot. 

3. Reassembly Procedures 

In the paragraphs that follow, the reassembly procedures for the M2 

will be covered. Refer back to figures 1 through 39 on pages 10 

through 36 in task 1 which dealt with dissassembly of the weapon. 

a. Detailed Reassembly. In the paragraphs that follow, the 

detailed reassembly procedures, starting with the receiver group, 

will be discussed. 

(1) Receiver Group. First, place the trigger lever in the 

receiver, with the long end forward and the bowed surface upward, 

between the top plate bracket and the bolt latch bracket. The 

trigger lever should project about 1/8 inch beyond the timer 

adjustment nut. Align the hole in the trigger lever with the holes 

in the receiver. Position the trigger lever pin assembly so that the 

key on the pin will pass through the keyway in the left sideplate. 

Push the trigger lever pin assembly all the way in and turn the pin 

90 degrees to the left, or counterclockwise. Turn the lock flat 

against the side of the receiver. Turn the lock which does not have 

a hinge counterclockwise until the lock fits in the small hole in the 

sideplate. 

59


Now install the cartridge stop assembly (or rear cartridge stop and 

link stripper) and front cartridge stop, on the right side of the 

receiver. Install the belt holding pawl pin. Place the belt holding 

pawl in position on the left side of the receiver, first seating the 

springs. Depress the pawl and insert the belt holding pawl pin. 

This completes the reassembly of the receiver. 

(2) Cover Assembly. Place the cover in the same position as for 

detailed disassembly. Hook the slotted end of the spring under the 

cover extractor stud with the projection pointing in the direction of 

its recess. Exercising caution, press down, and seat the projection 

of the spring in its recess in the cover extractor cam. 

Now place the cover latch spring inside the cover with the enlarged 

hole meshing with the cover latch spring stud, the hooked end down 

(resting on the cover extractor spring). Press down on the cover 

latch spring and slide it toward the latch. Pry up on the latch end 

of the spring, so that it rides up over the projecting wing of the 

cover latch. Snap the hooked end of the spring into its groove in 

the cover. 

Replace the belt feed pawl arm on the belt feed pawl. There are two 

pins on each side of the belt feed pawl. The larger is the belt feed 

pawl arm pin; the smaller is the belt feed pawl arm locating pin. 

For a left-hand feed, the belt feed pawl arm must be placed over the 

pins so that the belt feed pawl arm is toward the latch end of the 

cover, when the assembled side is returned to the cover. Place the 

small end of the belt feed pawl spring over the belt feed pawl spring 

stud (inside the belt feed slide). Place the assembled pawl and arm 

over the spring so that the large end of the spring is seated in the 

recess in the pawl, with the projecting oval (loop) of the spring 

away from the belt feed pawl arm. Align the pinholes in the pawl, 

arm, and slide; replace the belt feed pawl pin. Make sure that the 

pin is flush with the sides of the slide. Replace the belt feed 

slide in its guideways, with the belt feed pawl to the left, arm 

toward the latch. 

Now replace the shoulder headless pin and spring in their seats in 

the side of the belt feed lever. For left-hand feed, the spring and 

pin are seated in the hole nearest the belt feed lever lug. Now, 

60


place the belt feed lever over the pivot stud, lug up and to the 

left. With a thumb at either end of the lever, press down and turn 

the lever until the shoulder headless pin is against the inside of 

the cover. Pivot the lever until it is aligned with the slots of the 

cover and slide. Press the lever down as far as it will go. Move 

the lug end all the way to the right. Maintaining a downward 

pressure, snap the lug end all the way to the left so that the 

shoulder headless pin is properly positioned in the cover. Replace 

the lock pin (cotter pin) in the pivot stud, making sure that the toe 

end of the lever moves laterally in its slot without binding. 

To replace the cover group on the receiver, place the latch end of 

the cover in position, with the latch engaging the top plate. With 

the heel of your hand, tap the hinged end downward into position. 

Align the pin holes and replace the cover pin. Insert the cotter pin 

in the cover pin and spread the ends. This completes the reassembly 

of the cover group. 

(3) Barrel Extension Group. Replace the breech lock from the 

bottom of the barrel extension. Make sure that the wide, singlebeveled 

edge (or double-beveled edge) is up and to the front. In any 

case, the breech lock will be correctly positioned in its slot when 

the beveled edge is up and to the front, and the hole for the breech 

lock pin is toward the bottom of the barrel extension. Replace the 

breech lockpin so that the ends of the pin are flush with the sides 

of the barrel extension. This completes the reassembly of the barrel 

extension group. 

(4) Barrel Buffer Body Group. Replace the accelerator with the 

tips up and the claws to the rear. Replace the accelerator pin so 

that the ends are flush with the sides of the barrel buffer body 

group. Turn the barrel buffer body group upside down. Hold the 

assembly against the barrel buffer body group, lug down. With the 

thumb of one hand, press the forward winged part into the circular 

opening of the slot. With the other hand, raise the rear of the 

assembly enough to lift the lug over the buffer body. Push the 

assembly forward until the rear winged part (barrel buffer tube lock 

latch) snaps into the circular opening in the slot. This completes 

the reassembly procedures for the barrel buffer body group. 

61


(5) Bolt Group. Engage the rear end of the firing pin in its 

seating groove, located in the front end of the firing pin extension 

assembly. Insert the firing pin and extension assembly in the bolt, 

striker first, sear notch down. Push the extension assembly into the 

bolt, and tilt the front end down until the striker protrudes through 

its aperture in the face of the bolt. 

With the sear spring wedged on the cocking lever, replace the spring, 

and insert the sear in its slot-stud up, with the notch to the front. 

Make sure the sear spring is seated in its recess in the bolt, and 

the bottom of the sear. 

Press down on the sear and replace the sear slide in its guideways. 

The slide may be inserted from either side, unless the gun is to be 

fired by the sideplate trigger. In that case, the square end must be 

to the left. Replace the sear stop and pin (accelerator stop and 

lock). Press down on the head of the pin (base of the accelerator 

stop) to force it into place; swing the sear stop into its groove in 

the bolt. 

Replace the cocking lever, rounded nose down and to the rear with the 

top of the cocking lever to the rear. Replace the cocking lever pin 

from the left-side of the bolt. To test for correct assembly, cock 

the firing pin by rotating the top of the cocking lever toward the 

front of the bolt; then rotate it to the rear and depress the sear. 

This completes the reassembly procedures for the bolt group. 

This completes the detailed reassembly procedures for the M2 

machinegun. 

b. General Reassembly. In the next paragraphs, the general 

reassembly procedures for the weapon will be covered. 

(1) Barrel Buffer Assembly and Barrel Buffer Body Group. Replace 

the barrel buffer assembly, in the barrel buffer body group, with the 

key on the spring guide to the right. This key must fit in its slot 

in the right-side of the barrel buffer body. Turn the barrel buffer 

tube until the screwdriver slot (in the rear of the tube) is 

vertical, the arrow pointing to the right. The stud on the tube lock 

will now engage the serrations in the barrel buffer tube to keep the 

62


tube from turning. Now push the barrel buffer assembly fully forward. 

(2) Barrel Buffer Group and Barrel Extension Group. To join the 

two groups together, hold the barrel buffer group in the right hand, 

with the index finger supporting the accelerator. Join the notch on 

the shank of the barrel extension group with the cross-groove in the 

piston rod of the barrel buffer assembly. At the same time, align 

the breech lock depressors with their guideways in the sides of the 

barrel extension (claws against the shank) and push the groups 

together. As the accelerator rotates to the rear, press down on its 

tips to ensure positive locking of the groups. Place the groups in 

the receiver, and push them forward until the barrel buffer body 

spring lock snaps into position. When the parts are properly locked 

in place, the barrel buffer tube should protrude about 1 and 1/8 

inches from the rear of the barrel buffer body group. 

(3) Bolt. Place the bolt in the receiver, with the top of the 

cocking lever forward and the extractor down. Push the bolt forward 

into the receiver. As the front end of the bolt approaches the tips 

of the accelerator, lock in the sideplate of the receiver, press down 

on the rear end of the bolt to ensure the front end of the bolt 

clears the accelerator tips. Raise the rear of the bolt and continue 

to push the bolt forward until the bolt latch engages the notches in 

the top of the receiver. 

NOTE 

The barrel extension, barrel buffer, and bolt 

groups may be assembled and returned to the 

receiver together. 

(4) Bolt Stud. Align the bolt stud hole in the bolt with the 

clearance hole and replace the bolt stud, ensuring that the shoulder 

of the stud is inside the sideplate. 

(5) Driving Spring Group. Press up on the bolt latch and 

push the bolt all the way forward by pushing on the bolt stud 

only. Place the end of the driving spring rod in its hole in 

the rear of the bolt, and push forward on the driving spring 

group and barrel buffer tube. Press in and to the 

63


right on the head of the driving spring rod, and place the retaining 

pin in its seat in the right sideplate. 

NOTE 

At this time, the barrel buffer tube should be 

completely inside the receiver. If not, the 

barrel buffer body spring is not properly seated. 

(6) Backplate Group. Hold the backplate with the latch down and 

the trigger up; place the backplate guides in their guideways. Hold 

out on the latch lock and tap the backplate into position until the 

latch snaps into place. Release the latch lock, and pull up on the 

backplate group to ensure it is firmly seated. 

(7) Barrel. Pull the retracting slide handle to the rear until 

the lug on the barrel locking spring is visible through the 3/8 inch 

hole in the right sideplate. Place the smallest loop of a caliber 

.50 link, or suitable spacer, between the trunnion block and into the 

barrel extension; then unscrew the barrel two notches. Remove the 

link and close the cover. This completes the general reassembly 

procedures for the Browning caliber .50, M2 HB machinegun. 

After the weapon has been reassembled, be sure to coat frictional or 

sliding surfaces with either aircraft and weapons lubricant or 

general purpose lubricating oil (PLS). 

4. Final Inspection, Function, and Firing Test 

In the paragraphs that follow, the procedures used in performing the 

final inspection, function test, and the firing test will be covered. 

These procedures are necessary as they provide maintenance personnel 

with a means of double-checking their work to ensure that no defects 

were overlooked, that the weapon was reassembled correctly, and that 

it will operate in the proper manner. 

a. Final Inspection Procedures. First, visually inspect the 

machinegun to ensure that it is a complete and serviceable weapon. 

Inspect the exposed metal surfaces for dull rust-resistant 

64


finish, free from burrs and deep scratches. Ensure that the serial 

number is legible. Inspect all of the assemblies of the weapon to 

ensure that they are not loose. 

(1) Machinegun. Ensure that the weapon is complete and 

serviceable. Inspect all exposed metal surfaces to ensure that they 

contain a dull rust-resistant finish which is free of burrs and deep 

scratches. Make sure that the serial number is legible and that all 

assemblies are not loose. 

(2) Barrel Assembly. Inspect the barrel assembly to ensure that 

it is straight, clean, free of rust, powder fouling, bulges, and 

rings. Ensure that the serrations will be well defined so as to 

retain the barrel assembly setting by the locking spring. Ensure 

that the barrel carrier is secured to the barrel assembly. 

(3) Backplate Group. Make sure that the backplate group locks 

securely to the receiver group. Check the trigger, bolt latch 

release, latch and buffer tube sleeve for positive functioning. 

(4) Bolt Group with Rod Assembly. Ensure that the components are 

secure and properly positioned. The sear slide in the bolt should be 

assembled to the bolt from the left side (square end to the left). 

Make sure that the trigger lever does not drag on the bolt group when 

the trigger is depressed. Check the cartridge extractor for binding 

against the side plate. Make sure the ejector returns to the neutral 

position when it is pulled to the rear side and released. The firing 

pin and firing pin extension should move freely and align properly. 

Ensure that the sear and sear slide assembly function smoothly in the 

guideways without binding. Ensure that the driving spring rod 

assembly does not bind in the bolt group, also make sure that the 

driving spring rod locks securely to the side plate. 

(5) Barrel Buffer Group. The free ends of the breechblock 

depressors will have a slight vertical play, but no longitudinal or 

lateral movement. Ensure that the buffer body lock is not overstaked 

and that the guide is tight. Make sure that the buffer assembly 

contains no oil. Ensure that there is no binding between the 

accelerator claws and the depressors. 

65


(6) Barrel Extension Group. Ensure that the shank fits tightly 

and that the breechblock functions freely with a minimum of looseness 

in the slot. 

(7) Retracting Slide Handle. Make sure that the retracting slide 

handle is secured to the receiver group. Check the headless shoulder 

pin and the shouldered and stepped stud for looseness. Ensure that 

the retracting slide stud is firmly secured to the bracket. Check 

the helical torsion spring for correct positioning. Make sure that 

the retracting slide handle functions freely in the bracket and that 

it functions freely in its orbit. 

(8) M10 Charger. Visually inspect the M10 charger to ensure that 

it is secured to the correct side of the receiver group and that it 

is lockwired properly. Also ensure that it moves the bolt group to 

the rear and charges the machinegun. 

(a) Slide Group. Ensure that it moves through the full range 

of travel without binding. Make sure that the slide lock pawl lever 

engages and disengages the selector when the selector is manually 

operated. When the lever is disengaged from the selector, the slide 

shall lock in the rearward position. When the selector is engaged, 

the slide shall return to the forward position as the handle assembly 

is moved forward. Determine that the other components function as 

intended. 

(9) Rear Sight Assembly. The rear sight assembly should be 

secured to the top plate of the receiver group so that there will be 

no relative movement. Ensure that the leaf assembly moves manually 

between horizontal and vertical positions and that the sight assembly 

is held in either position under spring action until manually 

changed. Make sure that the elevating and windage adjustment knobs 

turn manually through their full range of travel, and produces 

positive retention perceptible by touch of each detent notch when the 

sight is adjusted. 

(10) Cover Group. Ensure that the bolt feed pawl spring with the 

oblong coil on the large end is positioned correctly. Also ensure 

that the cover operates freely in its travel. 

(11) R e c e i v e r G r o u p . M a k e s u r e t h a t a l l t h e 

r i v e t s a r e t i g h t . E n s u r e t h a t t h e b a r r e l s u p p o r t 

66


with applicable shim will be assembled to the trunnion block and 

locked into position. Ensure that the front sight cover and blade 

are firmly secured to the trunnion block. 

Determine that the bolt group does not bind and that the breech lock 

cam floats slightly. Ensure that the side plate switch nut is secure 

and that the switch does not bind. 

(12) Tripod Mount M3. Visually inspect the dial pointer for 

looseness. Check the upper elevating screw stop and traversing slide 

lock for proper functioning. Test the upper and lower elevating 

screws for binding. Now check the telescoping function of the upper 

and lower leg sections and the indexing lever assembly. Check the 

clamping action of the front leg clamp screw nut. Check that the 

serrations are in the proper alignment to ensure even spread of the 

legs when clamped. Check the function of the sliding sleeve and 

sleeve lock latch on the right rear leg, and the pintle and lock 

assembly. Finally, check the tension of the helical compression 

springs in the lock assembly. 

b. Function and Firing Test. In the following paragraphs, the 

function and firing test procedures employed by unit and IDS 

maintenance personnel to test the correct assembly and proper 

functioning of the machinegun will be discussed. 

The machinegun will be function tested by hand using 10 rounds of 

dummy ammunition. Upon completion of the hand functioning, the 

weapon will be test fired on a firing range or a provisioned firing 

range using 10 rounds of ball ammunition. 

Upon completion of firing, the machinegun will be properly cleaned 

and lubricated. The procedures for cleaning and lubricating the 

weapon were discussed in paragraph 2a(2) on page 45 of this task. 

Guns that fail to meet the functioning and firing tests are to be 

corrected by replacement of defective components. Upon completion of 

any additional repair work, the above procedures must once again be 

performed to test the weapon for correct assembly and proper 

functioning of components. 

67


5. Conclusion 

In this subcourse, the student was introduced to the components and 

operation of the M2, caliber .50 HB machinegun. Then the student was 

taken through the disassembly, inspection, repair, reassembly, and 

the final inspection and function tests used on this weapon. 

From the information presented in this subcourse, the student should 

be able to describe the components and operation of the M2 as well as 

explain the inspection and repair procedures used by unit and IDS 

maintenance personnel. It should be pointed out that this text is 

intended only as a learning guide and should not be used as a 

guideline for actually inspecting or repairing an M2 machinegun. 

68

M2 MACHINEGUN MAINTENANCE - OD1503 - LESSON 1/PE 1 

PRACTICAL EXERCISE 1 

1. Instructions 

Read the scenario and respond to the requirements that follow the 

scenario. 

2. Scenario 

You are the Armament Repair Section NCO of a Heavy Maintenance 

Company located in the Federal Republic of Germany. One afternoon 

around 1430 hours, your OIC who is the Armament Repair Technician 

notifies you that in approximately 60 days the maneuver elements of 

the division will be engaged in a month-long field training exercise 

(FTX). 

You have been directed to form a Maintenance Support Team (MST) and 

move down to the companies in one of the maneuver battalions. The 

purpose of this MST will be to inspect and/or repair all M2, caliber 

.50 machineguns in each of the companies. 

Since you have several days before leaving for the companies in the 

battalion, you decide to prepare a quiz to test the knowledge of your 

team concerning the M2 machinegun. Your OIC likes this idea and 

suggests that you take the quiz along and conduct some informal 

training with the unit supply specialist/unit armorers from each of 

the companies. 

3. First Requirement 

Below are the questions that you prepared to administer to the men of 

your MST and to the unit supply specialists/unit armorers. All that 

is left for you to do is to prepare an answer sheet for the quiz. 

Use your knowledge of the M2 machinegun and this subcourse to answer 

the questions below. 

a. When does locking begin in the M2 caliber .50 machinegun? 

b. Describe the procedures used when clearing the M2 machinegun. 

c. Describe the procedures for disassembling the barrel extension 

group. 

69


d. Briefly describe the M3 tripod mount. 

e. Describe the Preventive Maintenance Checks and Services. 

Inspection procedures used for the barrel assembly/group. 

f. Describe the procedures used for the care and cleaning of the 

weapon before, during, and after firing. 

g. How many buffer disks are there in the backplate assembly/group? 

h. The overall length of the buffer assembly (rear face of the tube 

to the forward inside face of the engaging notch) must be what? 

i. After the weapon has been reassembled and the final inspection 

procedures have been performed, the weapon should be hand 

functioned and test fired. How many rounds of dummy ammunition 

should be used when hand functioning the weapon? 

70


First Requirement 

LESSON 1. PRACTICAL EXERCISE - ANSWERS 

a. Locking begins 1 and 1/8 inches before the recoiling parts are 

fully forward. 

b. To clear the weapon first, unload the gun. This is done by 

unlocking the bolt latch release and raising the cover. Now the 

ammunition belt is lifted from the feedway. Now the bolt is 

pulled to the rear and the chamber and T-slot are examined to 

ensure that they contain no ammunition. After these steps have 

been performed, a wooden block extending approximately one inch 

above and below the receiver is inserted into the receiver 

between the bolt and the rear of the barrel. A cleaning rod is 

then inserted into the muzzle end of the barrel, pushed through 

the bore until it can be seen in the receiver, it is then 

immediately removed. 

c. First, drift the lockpin out and remove the breech lock from the 

bottom of the barrel extension group. 

d. The M3 mount is the standard ground mount for the M2 machinegun. 

It is a folding tripod with three telescopic, tubular legs, 

connected at the tripod head. The entire mount assembly weighs 

approximately 44 pounds. 

e. Inspect the bore with barrel reflector for rust, powder fouling, 

and obstructions. Check the barrel threads and locking notches 

for serviceability. Check the components of the barrel carrier 

assembly for serviceability. The retaining pin should be staked 

in the knob of the carrier assembly. The handle group should 

secure the carrier assembly firmly to the barrel assembly. 

f. First, disassemble the weapon into its major groups or 

assemblies. Clean the bore and the chamber, but do not oil them. 

Clean all the metal parts thoroughly and apply a light coat of 

oil to all the metal parts which do not come in contact with the 

ammunition. To ensure complete removal of powder residue and 

primer fouling from the bore of the machinegun barrel, 

71


the bore should be cleaned at least once a day, for at least 

three consecutive days after firing. The bore sweats out this 

fouling and residue, and cleaning must be repeated until there 

is no further evidence of sweating. 

g. There are 22 buffer disks in the backplate/assembly group. 

h. The overall length of the buffer assembly (rear face of the tube 

to the forward inside face of the engaging notch) must be 

between 6.086 and 6.117 inches. 

i. The weapon should be hand functioned using 10 rounds of dummy 

ammunition. 

72

M2 MACHINEGUN MAINTENANCE - OD1503 - REFERENCES 

REFERENCES 

73

M2 MACHINEGUN MAINTENANCE - OD1503 - REFERENCES 

REFERENCES 

The following documents were used as resource materials in developing 

this subcourse: 

FM 23-65 

TB 9-1000-247-34 

TM 9-1005-213-25 

74

MAINTENANCE OF THE M2 MACHINEGUN - Modern Prepper

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